The objectives of this study were to examine the feasibility of improving biogas production and process stability of anaerobic mono-digestion of food waste by co-digesting with MSW incineration plant fresh leachate, and to identify the key factors governing performance and stability of anaerobic digestion. For this purpose, a series of semi-continuous experiments were carried out. During a long-term operation period, contrary to the failure of mono-digestion of food waste, anaerobic co-digestion with fresh leachate exhibited a much better performance and stability in terms of high CH4 yields (375.9-506.3 mL/g VSadded), high VS removals (66.9-81.7%), no VFA inhibition, and stable pH (7.2-7.8). The unstable mono-digestion of food waste was recovered from process imbalance by supplementing trace metal elements (Fe, Co, Mo, Ni), as indicated by the increased CH4 yields (from 384.1 to 456.5 mL/g VSadded), the decreased propionate concentration (from 899.0 to 10.0 mg/L), and the increased pH (from 6.9 to 7.4). These results were in line with our analytical results that the food waste was deficient in trace metal elements, and fresh leachate was rich in them. Co-digestion strategy provided abundant trace elements for anaerobic process. Our results clearly demonstrated that the deficiency of metal elements was the reason causing the unstable performance of anaerobic mono-digestion of food waste, which was corrected by co-digesting with fresh leachate. This research provides a more technically and economically feasible approach to co-treating and co-utilizing food waste and fresh leachate from MSW incineration plant. (C) 2014 Elsevier B.V. All rights reserved.